Preheat oven to 400°F.
Sprinkle onion slices (about 1/2 cup) into a bake pan, pour in low sodium chicken stock (enough to cover bottom of pan) and arrange the rib racks, overlapping but not completely on top of one another. Add more onion slices and rosemary on top of the ribs and cover pan with foil.
Put ribs into a 400°F oven to start then turn down to 275°F to bake for about 2 hours, or until meat is fork-tender. Midway, remove foil and baste the ribs with pan juices (aroma fantastic!) and add a little more stock if bottom of pan is too dry.
When the ribs are done, remove foil and rosemary; pour BBQ sauce over the ribs. Place pan back into the oven at about 350°F until sauce is bubbling over the ribs (about 30 minutes).
Remove pan from the oven, let the ribs rest for about 5 minutes before cutting.
Serve and Enjoy!